1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to an LED (Light-Emitting Diode) light bar and a backlight module using the LED light bar.
2. The Related Arts
Liquid crystal display (LCD) has a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and is thus widely used. Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal panel and a backlight module. The operation principle of the liquid crystal panel is that liquid crystal molecules are interposed between two parallel pieces of glass and a plurality of vertical and horizontal fine electrical wires is arranged between the two pieces of glass, whereby the liquid crystal molecules are controlled to change direction by application of electricity in order to refract out light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided by the backlight module in order to normally display images. Thus, the backlight module is one of the key components of an LCD. The backlight module can be classified in two types, namely side-edge backlight module and direct backlight module, according to the position where light gets incident. The direct backlight module comprises a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), which is arranged at the back side of the liquid crystal panel to form a planar light source that directly provides lighting to the liquid crystal panel. The side-edge backlight module comprises a backlighting source of an LED light bar arranged at an edge of a backplane that is located rearward of one side of the liquid crystal panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face of the light guide plate and is projected out through a light emergence face of the light guide plate, after being reflected and diffused, to thereby form a planar light source for the liquid crystal panel.
In a heat dissipation arrangement of a conventional LED backlight module, LED chips are often soldered to a printed circuit board (PCB). The PCB is mounted to a heat dissipation strip by means of screws or thermally conductive adhesive. The heat dissipation strip is then mounted to a backplane. The PCB is often a metal core PCB (MCPCB) that shows improved heat dissipation or an FR4 substrate that comprises a copper layer and heat conduction through hole passage to improve heat transmission to a heat dissipation substrate. For the above two PCBs, the heat dissipation path of a backlight module is from the LED chips to a thermal interface material layer, and then sequentially through the PCB, a thermal interface material layer, the heat dissipation strip, and the backplane. Such a path is extended and shows poor heat dissipation performance due to PCB processing operation, so as to easily lead to over-temperature of the backlight module and thus affect the quality of backlighting.